An insight into the molecular and surface state photoluminescence of carbon dots revealed through solvent-induced modulations in their excitation wavelength dependent emission properties.

This study explores the intriguing modulations in the excitation wavelength dependence of carbon dot photoluminescence (PL), induced by the solvent medium. Our results indicate that different emissive states of carbon dots are stabilized to different extents by the surrounding solvent environment. Consequently, in some solvents, such as ethyl acetate and acetonitrile, the PL of the carbon dots is strongly dependent on the excitation wavelength, while in other solvents, like water, the PL of the same carbon dot becomes independent of the excitation wavelength. These observations contribute to the enhancement of our understanding of the photophysics and PL mechanisms of this important class of luminescent materials, especially to discriminate between the PL arising from the "molecular state" and the "surface state".

pH-Elicited Luminescence Functionalities of Carbon Dots: Mechanistic Insights.

Remarkable and systematic pH-dependent changes are observed in the absorption and emission spectra of carbon dots derived for the first time from lemon juice, a natural bioresource. Detailed photophysical studies of these novel carbon dots (henceforth termed LD), in conjunction with Fourier transform infrared spectra, reveal that among the two possible prototropic equilibria, phenol ↔ phenolate and carboxylic ↔ carboxylate, that occur at the surface of LD, it is the former that is actually coupled with the emissive moiety and directly involved in determining the nature of the electronic energy levels and the associated optical transitions. Apart from providing valuable mechanistic insights on the photoluminescence (PL) of carbon dots, the pH dependence of LD is also demonstrated to yield variable PL signals and perform elementary Boolean logic operations in response to chemical stimulants. The pH effect can therefore complement the optoelectronic functionalities of these promising luminescent nanomaterials and help in the future development of molecular devices and intelligent multianalyte detection systems.